Microfabrication has been carried out by lithography using a photoresist in the production of semiconductor devices. Here, the microfabrication is a processing method in which a photoresist thin film is formed on a semiconductor substrate such as a silicon wafer, active light such as ultraviolet light is applied onto the film through a mask pattern with a pattern of a device followed by development, the substrate is etched using the obtained photoresist pattern as a protective film, and a fine concave-convex structure corresponding to the pattern is consequently formed on a substrate surface.
In recent years, devices have been highly integrated, and the exposing light to be used has had a shorter wavelength, for example, a KrF excimer laser (a wavelength of 248 nm) and an ArF excimer laser (a wavelength of 193 nm). Such a change raises a problem of reducing dimensional precision of a photoresist pattern in a photolithography process by the effect of standing waves caused by reflections of exposed light from a substrate and by the effect of irregular reflections of exposed light due to level difference of a substrate.
To address the problem, a method of providing an anti-reflective coating (Bottom Anti-Reflective Coating, BARC) between a photoresist and a substrate has been widely studied.
Conventionally proposed anti-reflective coatings are typically formed using a thermally crosslinkable composition for preventing intermixing with a photoresist that is applied on the anti-reflective coating, and the formed anti-reflective coating is insoluble in an alkaline developer that is used for development of the photoresist. Thus, the removal of the anti-reflective coating prior to semiconductor substrate processing is carried out by dry etching (for example, see Patent Document 1), but the photoresist is also dry etched at that time. This makes it difficult to ensure a film thickness of the photoresist necessary for substrate processing and raises serious problems especially when a thin-film photoresist is used in order to improve resolution.
Meanwhile, as an ion implantation process in the production of semiconductor devices, a process of introducing impurity ions that impart n-type or p-type conductivity into a semiconductor substrate using a photoresist pattern as a mask may be adopted. In the process, it is undesirable to perform dry etching during the pattern formation of a photoresist in order to prevent the damage to a substrate surface. In other words, in the formation of a photoresist pattern for the ion implantation process, it is undesirable to use an anti-reflective coating that is required to be removed by dry etching as an underlayer of a photoresist.
However, a photoresist pattern that has been used as a mask in the ion implantation process has a comparatively large pattern line width and has been less affected by the standing wave caused by reflections of exposed light from a substrate or the irregular reflections of exposed light due to level difference of a substrate. Thus, by using a photoresist containing a dye or using an anti-reflective coating on a photoresist, the problems due to reflections have been solved.
However, as devices have a finer structure in recent years, a photoresist used in the ion implantation process has been required to have a fine pattern, and this has required an anti-reflective coating (resist underlayer film) on an under layer of a photoresist.
In view of such circumstances, there is a demand for the development of an anti-reflective coating that can be dissolved in an alkaline developer used for the development of a photoresist, does not require a dry etching process, and can be developed and removed concurrently with a photoresist, and there are some studies on such an anti-reflective coating (resist underlayer film) (for example, see Patent Document 2, Patent Document 3, Patent Document 4, Patent Document 5, and Patent Document 6).